The present invention relates generally to a method and an apparatus for wetting fibrous material as stated in the preamble of appended independent claims 1 and 9.)
Waste paper, from which cellulosic fiber material is to be reused, is processed to separate and recover clean fibers therefrom. Waste paper includes besides cellulosic fibers different types of contaminants, such as plastic, aluminum foils or wax used in layered paper or board, inks used in printing paper and also common dirt. The fibrous material in waste paper includes air between fibers, as well as, within the fibers themselves. Containers made of milk carton board and liquid carton board, i.e. layered material combining cellulosic fiber material with e.g. plastic material and/or Al-foil material, form a huge amount of waste material which needs to be recycled.
Typically waste paper mixed with a wetting agent is treated mechanically in a pulper or a slusher in order to disintegrate the paper and soak the fine paper material, fibrous material, until the fibers are sufficiently swollen to be separated.
The paper material may be soaked as long as it takes for all fibers therein to be completely wetted so that they may be washed or separated from any other material present in the paper, e.g. plastic, Al-foils, wax, ink etc. A long treatment, however, also tends to break or cut any non-fibrous material present in the waste paper into very fine particles, which fine non-fibrous particles are hard to separate from the cellulosic fibers. The particles are discharged with the accept fibers and transported to the next processing stage of the fibers which are to be recycled. Particularly plastic particles or Al-particles tend to cause severe problems in any such subsequent processing stage.
The beating treatment in a pulper also tends to affect the fibrous material itself. Long good quality fibers tend to break during the treatment, which leads to a decreased recycled fiber quality.
In order to prevent good quality fibers from being affected by the treatment and fine non-fibrous material (Al-foil or plastic) from entering subsequent processing stages the waste paper may be processed very gently and only for a short time period in the pulper. Such gentle treatment during a short time period only, however, leads to a very limited capacity of the recycling process. Up to 35% of the fiber material may remain unseparated and be discharged with the non-fibrous material without being recycled. This leads to increased cost of waste treatment. It is not only the fiber material mixed with e.g. Al-material which becomes impossible to use, it seems that also the Al-material becomes impossible to recover.
It is therefore an object of the present invention to provide an improved method and apparatus for wetting fibrous material in order to recover a maximal amount of good quality fibers.
It is particularly an object of the present invention to provide a method and an apparatus according to which fibrous material may be very rapidly separated from non-fibrous material, with a minimum deteoriation of the fiber material and with a maximal separation of contaminants.
It is also an object of the present invention to provide a method and an apparatus which provides an efficient wetting of fibrous material, such as cellulosic pulp in order to provide an efficient way of treating the fibrous material with desired additives, such as coloring agents, bleaching agents, surface tension decreasing agents or fire proofing agents or agents rendering the fibrous material hydrophilic or hydrophobic properties.
The above objects are achieved by a method and apparatus comprising features as stated in the characterizing portions of the appended independent claims 1 and 9.
A typical method for wetting fibrous material, such as coarsely shredded waste paper, comprises the steps of:
(a) introducing the fibrous material into a wetting enclosure;
(b) introducing wetting fluid into the wetting enclosure and allowing the fibrous material to be wetted by the wetting fluid;
(c) discharging a suspension of wetted fibrous material and wetting fluid from the wetting enclosure;
(d) decreasing the pressure within the wetting enclosure during step (a) or step (b) to a pressure p1 and
(e) after step (d) increasing the pressure within the wetting enclosure to a pressure p2 while keeping the fibrous material immersed in the wetting fluid.
In step (d) the pressure within the wetting enclosure is decreased e.g. by a vacuum pump or other ways of imposing a suction thereon. The pressure is preferably decreased to a pressure corresponding to 1-10 m water column. The wetting enclosure is thereby a vessel of the vacuum vessel type able to withstand vacuum as desired. The vacuum or low pressure brought about in the wetting enclosure forces air present in the waste paper, air within the fiber material and also air within the fibers itself, to be sucked out. Hollow empty spaces formed within the fiber material and within the fibers collapse. The fiber material, which at the beginning of the wetting process may have been floating on the surface of the wetting fluid is thereby immersed into the fluid.
Vacuum or low pressure may be established very rapidly, within a few seconds almost instantly, with a vacuum pump or other similar equipment known per se. The vacuum or low pressure is induced only for the very short period which it takes for air to be discharge from the fiber material as desired. As soon as the fibrous material is suitably immersed in the wetting fluid pressure is very rapidly increased in the wetting enclosure e.g. by allowing water or air to flow into the enclosure, the fibrous material being still immersed in the wetting fluid.
The increased pressure on the wetting fluid forces fluid to flow into collapsed empty spaces within the fibers and other cavities from which air was sucked out during the vacuum or low pressure treatment stage. Fibers swell rapidly as fluid penetrates into the fibers between different layers therein. The rapid swelling of fibers loosens the fibers from any non-swelling material, such as plastic or Al-foil material, to which the fibers may be bound to.
Steps (d) and (e) are preferably repeated at least once, more preferably several times. This can easily be done as the time span of steps (d) and (e) is very short. The decreasing and increasing of the pressure within the wetting enclosure may take place within an interval of  less than 1 minute, preferably  less than 30 seconds, most preferably  less than 10 seconds.
The present invention may be applied on a batch process or a continuous process. In a typical batch process a batch of the fibrous material is introduced into a wetting enclosure whereafter the pressure in the wetting enclosure is decreased and wetting fluid is introduced into the enclosure. Immediately thereafter the pressure in the enclosure is allowed to rise, e.g. to the atmospheric pressure level, whereby wetting fluid is sucked into hollow spaces and cavities in the fibrous material from which air was sucked out during the vacuum treatment stage. The fluid penetrating into the fibers causes the fibers to swell and thereby come loose from any material not subjected to similar swelling.
If desired the wetting agent may be introduced into the wetting enclosure before the vacuum treatment stage. Then a batch of the fibrous material and wetting fluid is introduced into a wetting enclosure whereafter the pressure in the wetting enclosure is decreased to a desired level to suck out air from the fibrous material. Thereafter the pressure in the enclosure is allowed to rise again to force wetting fluid to be sucked into hollow spaces in the fibrous material.
It is also possible to arrange for a continuous process, in which
a flow of fibrous material and a flow of wetting fluid is continuously fed into a first wetting enclosure having a subatmospheric pressure p1 therein, in which enclosure the fibrous material is treated by vacuum so that air is sucked out of the fibrous material,
a flow of mixed vacuum treated fibrous material and wetting fluid is continuously fed from the first wetting enclosure into a second enclosure having a pressure p2 therein, the pressure p2 being  greater than p1, in which second enclosure wetting fluid is sucked into the fibrous material and into hollow spaces within the fibers, the fibers thereby being wetted and swollen,
a flow of mixed wetted fibrous material and wetting fluid including separated fibers is discharged from the second enclosure into a separator in which accepted fiber material is separated from contaminants, e.g. non-fibrous material, and
a flow of a suspension of accepted fiber material and wetting fluid is discharged from the separator separately from a flow of contaminants.
If desired a flow of mixed partly wetted fibrous material and wetting fluid may be introduced from the second enclosure into a third enclosure for a second vacuum treatment stage and further from the third enclosure into a fourth enclosure having a higher pressure therein than the pressure in the third enclosure. A flow of mixed fully wetted fibrous material and wetting fluid is then discharged into a separator. If needed the fibrous material may be transported through more than two consecutive vacuum treatment stages, e.g. 3 to 5 different vacuum stages and corresponding higher pressure stages therebetween, until the fibrous material is sufficiently wetted.
A continuous wetting process may be performed as described by transporting a flow of fibrous material through e.g 3 to 10 separate consecutive treatment vessels. Wetting fluid or other fluid may be added into the flow during any of the separate stages or material may be discharged from any of the separate stages.
A continuous wetting process may on the other hand be performed in a single vessel divided into separate pressure tight compartments through which a flow of fibrous material and wetting agent is forced to flow. A vessel of a screw conveyor type could be used.